async _initializeDecryptionMaterial()

in modules/material-management-browser/src/browser_cryptographic_materials_manager.ts [157:211]
43 lines of code
3 McCabe index (conditional complexity)

  async _initializeDecryptionMaterial(
    suite: WebCryptoAlgorithmSuite,
    encryptionContext: EncryptionContext
  ) {
    const { signatureCurve: namedCurve } = suite

    /* Check for early return (Postcondition): The WebCryptoAlgorithmSuite specification must support a signatureCurve to extract a verification key. */
    if (!namedCurve) {
      /* Precondition: The context must not contain a public key for a non-signing algorithm suite. */
      needs(
        !Object.prototype.hasOwnProperty.call(
          encryptionContext,
          ENCODED_SIGNER_KEY
        ),
        'Encryption context contains public verification key for unsigned algorithm suite.'
      )

      return new WebCryptoDecryptionMaterial(suite, encryptionContext)
    }

    /* Precondition: WebCryptoDefaultCryptographicMaterialsManager If the algorithm suite specification requires a signatureCurve a context must exist. */
    if (!encryptionContext)
      throw new Error(
        'Encryption context does not contain required public key.'
      )

    const { [ENCODED_SIGNER_KEY]: compressPoint } = encryptionContext

    /* Precondition: WebCryptoDefaultCryptographicMaterialsManager The context must contain the public key. */
    needs(compressPoint, 'Context does not contain required public key.')

    const backend = await getWebCryptoBackend()
    const subtle = getNonZeroByteBackend(backend)
    const webCryptoAlgorithm = { name: 'ECDSA', namedCurve }
    const extractable = false
    const usages = ['verify'] as AwsEsdkJsKeyUsage[]
    const format = 'raw'

    const publicKeyBytes = VerificationKey.decodeCompressPoint(
      fromBase64(compressPoint),
      suite
    )
    const publicKey = await subtle.importKey(
      format,
      publicKeyBytes,
      webCryptoAlgorithm,
      extractable,
      usages
    )

    return new WebCryptoDecryptionMaterial(
      suite,
      encryptionContext
    ).setVerificationKey(new VerificationKey(publicKey, suite))
  }